You're right. Even though both systems are handheld consoles they are appealing to different groups.
But the PSV sure needs to play to its strengths. The 3DS is not taking off because the need for 3D in many of the games that plays well on the DS is not really essential.
Its a fair point, but the reason for the failing grade is that the developer should know better. There were higher expectations on DNF because the last game was so good and this one was not. The gameplay itself was disjointed and not enjoyable. While the game is amusing at times, it was not fun.
Taking a franchise and putting out a bad product with its name slapped on it is also worth being failed to protect the consumer and to send a message to the publisher.